Method and apparatus for trueing marine propellers



June 19, 1962 G. DEN HERDER 3,039,512

METHOD AND APPARATUS FOR TRUEING MARINE PROPELLERS Filed Feb. 23, 1960 2 Sheets-Sheet 1 Gerald Den H rde r zvmvron.

June 19, 1962 G. DEN HERDER 3,

METHOD AND APPARATUS FOR TRUEING MARINE PROPELLERS Filed Feb. 23, 1960 2 Sheets-Sheet 2 Gerald Den Herd e I IN V EN TOR.

ilnited States Patent 3,039,512 METHOD AND APPARATUS FOR TRUEING MARINE PROPELLERS Gerald Den Herder, 9235 N. Edison, Portland, Oreg. Filed Feb. 23, 1960, set. No. 10,350 7 Claims. (Cl. 153-32) This invention relates to method and apparatus for trueing marine propellers.

As is well known, marine propellers of all types and sizes are subject to damage from striking submerged objects. Where the damage is not too great, the propeller usually is repaired and re-used.

To restore the propeller to its original and useful condition, it is necessary that it be corrected for pitch, blade angle, and track. By pitch is meant the angle the blades assume with respect to the plane of the propeller. By blade angle is meant the angle present between the blades, i.e. 120 for a three-bladed propeller. By track is meant the location of the blades in the same plane so that, as the propeller rotates, one blade follows precisely behind the preceding blade in the same path.

The priorart procedures for repairing propellers have consisted of mounting the propeller on an arbor and hammering the blades lustily one at a time until some degree of correction has been attained, as determined by the use of bevel squares or pitching dies. Obtaining a true pitch has been practically impossible of achievement, since the blades are stiff and resistant, and since they have a pronounced tendency to spring back after each hammer blow.

This problem has been particularly acute with outboard motor propellers provided with a rubber sleeve between the hub and the blade assembly which permits the latter to slip upon striking an obstruction, reducing correspondingly the likelihood of damaging the propeller. As a result, it has not been feasible heretofore in the average propeller repair shop to pitch propellers with a high and requisite degree of precision. Furthermore, correcting the blade angle and tracking qualities of the propeller customarily has been but indifferently approximated.

It is the general object of the present invention to provide a rapid, easily effectuated method for trueing marine propellers, i.e. for correcting them for pitch, blade angle and track, with a high degree of precision.

It is another important object of this invention to provide apparatus for trueing marine propellers, which apparatus is simple in construction, easily used, and generally applicable in the average propeller repair shop to marine propellers of the usual categories and sizes and especially to the propellers of outboard motors.

The manner in which the foregoing and other objects of the invention are accomplished will be apparent from the accompanying specification and claims considered together with the accompanying drawings, wherein like numerals of reference indicate like parts and wherein:

FIGS. 1 and 2 are plan and side elevations respectively, FIG. 2 being partly in section, of the herein described apparatus for trueing marine propellers;

FIGS. 3 and 4 are detail sectional views illustrating means of mounting propellers used on outboard motors and inboard motors respectively;

FIG. 5 is a fragmentary sectional view illustrating the manner in which a bent propeller blade lies on a pitching die used in conjunction with the apparatus of the present invention;

FIGS. 6 and 7 are plan and side elevational views, respectively, FIG. 7 being partly in section, illustrating apparatus employed in determining propeller blade angle and track by the presently described method; and

FIGS. 8 and 9 are plan and side elevational views, respectively, of the apparatus of FIGS. 6 and 7 as applied to a marine propeller.

In general, the presently described method of trueing marine propellers having bent blades comprises rotatably mounting the propeller on the propeller pitching die, certain areas of the blade being spaced from the die face and certain other areas being in contact therewith as a result of the bending of the blade. Clamping pressure is applied to the propeller, after which the blade is straightened against the die face.

During the straightening operation, the clamping pressure is adjusted as required to permit the propeller to rotate in the direction of the die only as it is straightened, thereby preventing spring-back and insuring true pitch. The various blades of the propeller then are pitched in succession in the manner described, simultaneously conforming the angle between the blades to the theoretical desired angle, and shaping the blades to a configuration which tracks perfectly.

Considering the foregoing in greater detail and with particular reference to the drawings:

In FIGS. 1-5 is illustrated apparatus for executing the basic propeller blade-pitching method of my invention, while in FIGS. 69 inclusive is illustrated apparatus which may be employed in imparting not only true pitch to propeller blades, but also the correct blade angle and tracking qualities.

Turning first to the apparatus illustrated in FIGS. 15:

The apparatus of the invention is mounted on a worktable 111 and is used in conjunction with a conventional propeller pitching die 12. The latter is provided with a base 14 and a die segment 16, the upper surface 18 of which is pitched to conform to the theoretical pitch of the blades on the propeller to be repaired.

Two types of propellers are illustrated in the drawings. Propeller 20 (FIGS. 1, 2 4, and 5) includes a hub 22 and three blades 24, spaced at an angle of from each other. A tapered bore 26 extends longitudinally through the hub and is designed to accommodate a tapered propeller shaft in the usual manner.

Outboard propeller 2% (FIG. 3) likewise includes a hub 30 and blades 32. Hub 30, however, is provided with a rubber sleeve 34 inside which is located a bushing 36 defining a cylindrical bore 38. The latter accommodates the shaft of the outboard engine in the usual manner. The blade assembly is designed to slip about rubber sleeve 34 in the event an obstruction is struck, thereby minimizing damage to the blades. As has been noted above, they are particularly difiicult to pitch properly because of this fact.

Means are provided on the die for mounting the propeller thereon. Base 14 is formed with a pair of spaced vertical recesses 49 dimensioned to receive a corresponding pair of spaced pins 42 extending downwardly from a mounting block 44. This block is formed with a cylindrical axial opening which receives a spindle or arbor 46 upon which the propeller is rotatably mounted. In the embodiment of FIG. 4, arbor 46 has a tapered, stepped configuration as required by the tapered bore of the propeller hub. The segment of the arbor of reduced diam- .eter seats in the bore of block 44 and the tapered under section of enlarged diameter seats in the bore of propeller hub 22.

Similarly, in the case of the outboard propeller illustrated in FIG. 3, a'spindle or arbor 48 is provided having a stepped cylindrical configuration, the lower segment of restricted diameter being received in the bore of block 44 and the upper segment of enlarged diameter in the bore 0 of propeller hub 30.

peller hub as required to clamp it against block 44 while still permitting its selective rotation in one direction only. In the illustrated form of the invention, such pressure is applied through a cap piece 50 having a recessed upper surface and adapted to bear upon the planar upper surface of the propeller hub. The recess in the upper surface of the cap piece receives a ball member 52 which is fixed to one end of a lever arm 54.

Lever arm 54 is fulcrumed intermediate its ends by being supported on a laterally extending pivot pin 56 which preferably is mounted in means for securing vertical adjustment of the lever assembly in order to accommodate propellers and dies of varying height.

To this end there may be provided a post 58, the base of which extends through work table and is secured by nut 60. The upper end 62 of the post is provided with a longitudinally extending guideway 64 in which are mounted slidably a pair of opposed bearing blocks 66 mounting between them for angular movement of arm 54 the pivot pin 56 attached thereto.

A screw 68 is threaded into the top of post 62 and bears against the upper surface of the uppermost of bearing blocks 66. It is operated by a crank 70.

Screw 68 works against the resilient pressure exerted in an opposite direction by resilient means such as compression spring 72 mounted in the lower part of guideway 64. In this manner there is provided fulcrum mounting means whereby lever arm 54 may be adjusted vertically as required by the size of the particular propeller to be repaired.

Means also are provided for exerting a predetermined pressure on the hub of the propeller on die 16. Accordingly there are provided jack means such as hydraulic jack 74, the base of which rests on table 10 and the recessed end of the piston rod 76 of which engages a ball member 78 corresponding in function to ball member 52, but fixed to the opposite end of lever arm 54. Thus, operation of jack 74 by means of lever 80 applies the desired pressure to the propeller hub.

When pitching propellers using the apparatus of FIGS. l5, the propeller first is mounted on the apparatus in the manner indicated in the drawings. However, if the blade to be corrected is bent upwardly in such a manner that it would contact the die only at or near the propeller hub, the propeller is mounted in the first instance with the bent blade clear of the die. The propeller is clamped securely by operation of jack 74 and the blade hammered until it is bent downwardly instead of upwardly. This will bend the blade in such a manner as to provide it with what may be termed a preformed cavity or hollow facing the working surface of the die, if such a cavity, or hollow, already is not present in the blade as a result of the deforming accident.

The clamping pressure exerted by the jack then is released and the propeller rotated until the downwardly bent blade lies across the die face. As indicated in FIG. 5, certain areas on the outer portion of the blade then will be in contact with the die face while others are spaced from it, i.e. the blade will be arranged with the pre-formed cavity cupped over the die face. The objective now is to bring all of the blade area in contact with the die face in order to pitch it correctly.

To achieve this objective, the bent blade is straightened against the die face by judicious hammering with a suit able mallet. This will require that the propeller rotate about its axis in a direction which will advance the blade toward the die face, i.e. in a blade-straightening direc tion. This result is achieved by adjusting the pressure exerted by jack 74 in such a manner that upon hammering the blade, the propeller will rotate in the desired direction, but will be inhibited from rotating in the reverse direction.

It will be apparent that, when the correct amount of pressure is applied by means of jack 74, the reversing force exerted by the spring-back tendency of the blade,

not being as great as the driving force of the hammer blows, will be unable to rotate the propeller in the reverse direction. As a result, the blade is advanced incrementally toward the die face with contemporaneous rotation of the propeller as required to permit such advancement.

After the blade has moved from the position of FIG 5 to the position of FIG. 2, where it is flush against the die face and of correct pitch, the entire blade is swaged with the hammer until the bends in it have been set and no spring-back is noted upon releasing the pressure of jack '74. This relieves the internal stresses in the metal so that the blade will remain truly pitched even after removal from the apparatus. When this has been accomplished, lever 54 may be released and the propeller rotated manually until another bent blade lies across the face of the die. It, as well as the remaining blade, may then be pitched in the same manner as the first blade.

In FIGS. 69 is illustrated apparatus which may be used in conjunction with the pitching apparatus of FIGS. 15 in correcting the propeller for between-blades angle and blade tracking contemporaneously with the pitching operation. This apparatus is used in conjunction with a pitching die, which, like the die illustrated in FIGS. 15, comprises a base 14, a die section 16, and a die face 18. When using the die, the propeller is mounted on a support block 44.

Also included in the assembly, however, is an arm extending radially from the die, the inner end of the arm being provided with a pair of spaced, perforations through which pass locating pins 42 of support block 44, thereby anchoring the arm in position.

Supported on arm 9% is a vertically extending indicating finger comprising a bar 92 from the lower inner side face of which extends a small plate 94-. A permanent magnet 96 is adherently or otherwise atfixed to the under side of the plate for releasably mounting the finger on arm 90.

Finger 92 provides a means for establishing a first reference point adjacent the die and is used in conjunction with protractor or angle-measuring means mounted on block 44. The angle-measuring means is supported in vertically spaced relation to the block by means of an arbor or spindle 98, the lower enlarged section 100 of which seats in the bore of block 44- and the centrally located annular flange 102 of which seats on the upper surface of the block.

Fixed to the upper segment 104 of spindle 93 are a pair of integral arms 166, 108, the opposite outside edges of which are straight and separated by an angle which is exactly the between-blades angle of the propeller to be corrected. In the case of a three-bladed propeller, this angle obviously will be 120", as illustrated in the draw ings.

Also included in the assembly, but not illustrated in FIGS. 69, is means for applying pressure to the hub of a propeller mounted thereon, e.g. the vertically adjustable, jack-operated lever arm 54 of FIGS. 1-5.

When trueing propellers usin the above described apparatus, arm 90 and block 44 first are mounted on the die base. Finger 92 is located on arm 90 with its inner, lower, side face snug against the outer edge of the arm. It is maintained in position by magnet 96.

Spindle 98, supporting angle-measuring arms 106, 108, is mounted on block 44 with the outer edge of arm 106 aligned with the outer edge of the support arm and contacting the upper inner face of finger 92. This establishes a reference point for the angle-measuring procedure.

Next a line 110 is scribed on die surface 18 along the outer edge of arm 108. This line will lie at exactly from finger 92.

The angle measuring assembly including arms 106, 108 then is removed from support block 44 and propeller 20 mounted thereon. Pressure is applied to the propeller hub using cap piece 50 and jack-operated lever arm 54 in the manner illustrated in FIGS. 1-5.

The first propeller blade next is pitched against the die face. The outline of the pitched blade is scribed on the die face, the line being indicated at 112 of FIG. 8. Line 110 on the die face then is extended as line 114 on the propeller blade.

After this has been accomplished, and after the pressure of lever arm 54 has been released, the propeller is rotated clockwise, as viewed in FIG. 8, until the second blade lies across face 18 of the die and reference mark 114 is exactly aligned with finger 92, as shown in FIG. 9. The second blade then is pitched by hammering it against the die face until its surface exactly conforms to the angle of the die face and until its outline fits within outline 112 of the first blade. Line 110 on the die face is extended onto the blade, the pressure of lever arm 54 released, and the propeller rotated again until the third blade lies across the die face. This blade then is corrected in the same manner.

By this sequence of operational steps, not only is a true pitch imparted to the blades, but their spacing from each other is adjusted to the theoretical value. Still further, the blades are made to lie directly behind each other and will follow the same pitch, i.e. track properly, when the propeller again is placed in operation. The result is a propeller which has been restored completely to its original condition and will operate eificiently and without vibration.

It is to be understood that the form of my invention herein shown and described is to be taken as a preferred example of the same and that various changes in the shape, size and arrangement of parts may be resorted to without departing from the spirit of my invention or the scope of the subjoined claims.

Having thus described my invention, I claim:

1. The method of trueing marine propellers having at least one deformed blade bent to provide a pre-formed cavity, which method comprises: rotatably mounting the propeller with the deformed blade positioned against a propeller pitching die, the pre-formed cavity being cupped over the die face and hammering the blade against the die while applying to the propeller a clamping pressure sufiicient to permit the propeller to rotate in the direction of blade straightening under the force of the hammer blows, but to restrain the propeller from springing back in the interval between hammer blows, thereby advancing the blade incrementally toward the die with each hammer blow until it is flush with the die and of true pitch.

2. The method of claim 1 wherein the propeller is maintained in a fixed plane while all of its blades are straightened by hammering, one at a time, thereby insuring proper tracking of the blades.

3. The method of trueing marine propellers which comprises establishing a first reference point adjacent a propeller pitching die, establishing a second reference point on the die face at a predetermined propeller blade angle to the first reference point, rotatably mounting the propeller in a given plane with a first blade thereof on the die face opposite the second reference point, straightening the first blade against the die face, outlining the straightened first blade on the die face and marking its exposed face opposite the second reference point, rotating the propeller until the mark on the straightened first blade thereof aligns with the first reference point and the second blade thereof is located on the die face opposite the second reference point, straightening the second blade against the die face until it falls substantially within the outline of the first blade described thereon, while maintaining the mark on the straightened first blade aligned with the first reference point, and thereafter repeating the foregoing sequence for the remaining blades of the propeller, thereby adjusting them to positions of true pitch, spacing, and tracking relative to each other.

4. The method of claim 3 wherein a predetermined degree of clamping pressure is applied to the propeller hub as each blade is straightened against the die, thereby permiting the blade to advance toward the die while restraining it from springing back and insuring that it attains the true pitch of the pitching die.

5. Apparatus for use in trueing marine propellers by hammering, said apparatus comprising a propeller-pitching die, support means rotatably supporting a propeller in a fixed plane adjacent the die for positioning a blade of the propeller against the working surface of the die, and pressure-applying means comprising an hydraulic cylinder positioned for applying pressure to the propeller hub in an amount predetermined to permit rotation of the propeller on the die in the direction of blade straightening while restraining the propeller from springing back in the interval between hammer blows.

6. Apparatus for use in trueing marine propellers by hammering, said apparatus comprising a propeller-pitching die, support means rotatably supporting a propeller in a fixed plane adjacent the die for positioning a blade of the propeller against the working surface of the die, and pressure applying means comprising a lever arm fulcrumed intermediate its ends, bearing means on one end of the lever arm for hearing against the propeller hub, and jack means applied against the other end of the lever arm for applying the predetermined amount of pressure thereagainst.

7. The apparatus of claim 6, including mounting means for the fulcrum of the lever arm, the mounting means being adjustable to permit lateral movement of the lever arm as required to position the propeller on the die.

References Cited in the file of this patent UNITED STATES PATENTS 

